For decades, there have been modifications of the proportions of alloying elements in the copper-beryllium-nickel and/or cobalt systems and changes in thermomechanical processing in attempts to impart an especially desirable combination of engineering characteristics, heretofore unavailable, with varying degrees of success.
U.S. Pat. No. 2,289,593 teaches a ternary age hardenable copper-based alloy containing various proportions of beryllium and nickel (up to 4.25% nickel and 0.8% beryllium) that is characterized by improved conductivity which can be especially utilized in welding electrodes.
U.S. Pat. No. 4,179,314 relates to an age hardenable copper-based alloy containing beryllium, cobalt and/or nickel and minor amounts of other elements (up to 3.5% nickel and 0.2 to 1.0% beryllium) that undergoes thermomechanical treatment to enhance conductivity and mechanical properties at elevated temperatures, especially intended for rotor wedges for electrical generators.
U.S. Pat. No. 4,657,601 teaches a thermomechanical process for making an age hardenable copper-based alloy containing beryllium, cobalt and/or nickel and minor amounts of other elements (0.2 to 0.7% beryllium and 1.0 to 3.5% nickel and cobalt) which produces an improved combination of strength, ductility, formability and conductivity for alloys in strip form intended for the production of spring connectors, among other uses.
An important consideration in the manufacture of strip which is intended for use in various connector applications is the capacity of the material to be formed or bent into useful shapes without cracking. The degree of formability of the material, i.e., the ability of the material to be bent and shaped without fracture, is assessed by dividing the minimum bend radius having no cracking when the material is bent 90.degree. or 180.degree. ("R") by the thickness of the material ("T"). This is known as the R/T ratio. The axis of the bend in the material is made either parallel to or perpendicular to the rolling direction of the strip.
Copper-based alloys such as phosphorus-bronze that derive their strength principally from cold working, that is, deformation below the annealing temperature to cause permanent strain hardening, typically exhibit disparate R/T ratios depending upon the particular bend orientation and strength level of the alloy. Mill hardened copper-beryllium alloys at higher strength levels (greater than 100 ksi TS) are characterized by more nearly isotropic formability than the cold worked alloys as described in Getting Full Value From Beryllium Copper in Connector Design (1982), published in the Proceedings of the 15th Annual Connectors and Interconnection Technology Symposium (1982).
A family of lower cost, high conductivity copper beryllium connector alloys does exist in which the formability in one direction is significantly different in a transverse direction. U.S. Pat. No. 4,551,187 reports parallel axis to perpendicular axis bend 90.degree. R/T ratios from 3:1 to 9:1. U.S. Pat. No. 4,657,601 cites parallel axis bend to perpendicular axis bend 90.degree. R/T ratios between 2:1 and 9:1.
Therefore, there is a need in the art for an age hardenable copper-beryllium alloy which produces enhanced levels of formability (lower R/T ratios), especially in the direction parallel to the rolling direction, together with conventional levels of strength, ductility, stress-relaxation and electrical conductivity.